1. Field of the Invention
The present invention relates to a method of fabricating a fin field effect transistor (finFET), and more particularly, to a method of fabricating a finFET having strained channel region.
2. Description of the Prior Art
As semiconductor devices switching speeds continuing to increase and operating voltage levels continue to decrease, the performances of metal-oxide-semiconductor filed effect transistors (MOSFETs) and other types of transistors, need to be correspondingly improved. Currently, along with the development of the MOSFETs, one of the main goals is to increase the carrier mobility so as to further increase the operation speed of the MOSFETs.
In general, a MOSFET is disposed on a semiconductor substrate, which has at least a gate structure, a source region, a drain region separately disposed on two sides of the gate structure and a channel region disposed in the semiconductor substrate right below the gate structure. When a voltage with a certain value is applied to the gate structure, the resistance of the channel region decreases correspondingly, due to the induced capacitance effect and to the carriers that are able to flow between the source region and the drain region freely. In theory, it is well-known that the mobility of carriers flowing in the channel region can be affected by a lattice structure within the channel region. In order to get benefits from this phenomenon, in the current fabrication processes, a stress layer will be formed on a semiconductor substrate to cover a corresponding gate structure, a source region and a drain region, so as to transfer or apply the inherent stress to the predetermined channel region disposed below the gate structure. However, to carry out a heat treatment process is necessary for the stress transferring process, and this process will bring heat effect to the device on the semiconductor substrate, inducing process variation and side effect. In addition, since there is still a gate structure disposed between the stress layer and the predetermined channel region, the effect of stress transferring process is limited. As a result, it is still an important issue for the manufacturer to provide a method of fabricating FET that the inherent stress of the stress layer can be directly transferred to the corresponding channel region more effectively without inducing process variation.